Sometimes you know you'll attend a wedding long before you receive the invitation in the mail. Other times, the struggle is real — your pen hovers over the reply card, wavering between the "will attend" and "declines with regret." But is it ever okay to decline? For the answer, we turned to the experts.

"Before replying 'no,' it's important to consider the relationship you hold with the [couple], and how it will affect your relationship if you choose to skip the wedding," offers Diane Gottsman, etiquette expert. "If it's an immediate family member or a very close friend, it's an invitation you should weigh carefully before saying no."

But if the answer is still unclear, experts agree these are the three times it's okay to decline:

1. It's a destination wedding. "Couples who are planning destination weddings expect this," explains Julie Blais Comeau, etiquette expert and the author of Etiquette: Confidence & Credibility. Some may even have a waiting list — a second string of guests they will invite as regrets come in. "Depending on your relationship, you may or may not share that the reason you will not be attending the festivities is financial," Comeau adds. "Should you choose to, it is best to do so in person. The couple may even know of a cousin who can offer you a ride, or a neighbor that has a spare room for that weekend."

2. You have a prior commitment that you can't reasonably reschedule, such as a pre-booked, prepaid family vacation, or an important business event that others are relying on you to attend. "Let the couple know there are circumstances out of your control, and you will do whatever you can to help before the big day," Gottsman suggests. "A good friend will understand."

3. Attending would cause you emotional distress. "For example, if your former sister-in-law invites you to her wedding, you may not want to attend because you don't want to see your ex," offers Gottsman. "Or perhaps you would say no to being a bridesmaid when you know you can't give the duty the responsibility or time it deserves."

There's also one time it's never okay to decline, experts say: You're currently in a petty argument with the bride or groom, something that will within days or weeks blow over. "While you should never feel obligated to attend a wedding you don't want to be a part of, think carefully if the reason you are using will hold up years later when you look back on it," Gottsman says.

Once you decide to decline, you should ideally share the news in person, not through the mail. "Start your wedding invitation regrets by thanking your friend for inviting you," says Comeau. "Don't lie or make up a story, especially if this is a close friend. Explain the reality of your business calendar, family situation or financial difficulties. But there's no need to go on and on — keep it short and to the point."

If you've already purchased it, this is a great time to give the bride and groom their wedding present, too. "Remember, declining a wedding invitation does not liberate you from the obligatory wedding gift," Comeau says.

Have you ever declined a wedding invitation? Why? Tell us on Twitter at @Brides!